The present invention relates to a method for assembling a semiconductor package and a semiconductor package assembled by such a method. In particular, the present invention relates to curing and rapidly cooling an encapsulation material that encapsulates a semiconductor die that is a component of the package.
Typical semiconductor packages are formed with a semiconductor die mounted to either a lead frame or a removable support substrate (e.g., removable tape) supporting an arrangement of external connection pads and an optional flag. When a semiconductor package is formed from a semiconductor die mounted on a support substrate, the semiconductor package is usually referred to as a Flat No-lead package such as a Quad Flat No-lead (QFN) package or a Dual Flat No-lead (DFN) package.
The manufacture of Flat No-lead semiconductor packages includes encapsulating the semiconductor die and external connection pads with an encapsulation material. The encapsulation material is typically a molding compound that is cured and then gradually cooled from a curing temperature to room or ambient temperature. These two steps are called cure and post-mold cure. During post-mold cure, the package is maintained under pressure with a clamping device and gradually cooled using ambient air. However, it has been found that during such gradual cooling the semiconductor package can deform due to differences in coefficients of thermal expansion (CTE) of the semiconductor die and the substrate and the molding compound. More particularly, these CTE mismatches can cause an upper surface of the encapsulation material to become slightly domed (convex) and a corresponding base surface of the encapsulation material also to become slightly domed (concave). Unfortunately, the slightly domed upper surface is undesirable as the upper surface ideally should be flat so that a suction robot arm can pick up the package for post curing processing. Further, the slightly domed base surface can cause the external connection pads to be non-planar, resulting in poor quality solder connections of the external connection pads to mounting pads of a circuit board. Thus, it would be advantageous to be able to assemble a semiconductor package that is not warped during post-mold curing.